The increasing demands placed on the preservation and economical use of natural resources at the present time have necessitated a cut in the consumption of energy for refrigeration and freezing of foodstuffs in obtaining low temperatures with the aid of suitable apparatus.
Higher requirements are also imposed on the operational reliability of apparatus used for obtaining low temperatures in stringent operating conditions, and also at the end of the refrigeration or freezing process, when the heat loads are minimal.
Known in the art is a method of obtaining low temperatures (cf. USSR Inventor's Certificate No. 800,519, cl. F25B, 1979) by pulse-feeding a refrigerant, forming refrigerant vapours at a low pressure, compressing the refrigerant vapours from a low to a high pressure, condensing the refrigerant vapours until the formation of a liquid refrigerant and boiling thereof at a low pressure and a boiling temperature out of the range of boiling temperatures corresponding to the final temperature of the refrigerated medium. According to this method, the liquid refrigerant boiling temperature range is set as the difference between the temperature of the refrigerant vapour condensation prior to the formation of the liquid refrigerant, and the boiling temperature thereof as corresponding to the final temperature of the refrigerated medium.
There is also known in the prior art apparatus for obtaining low temperatures (cf. USSR Inventor's Certificate No. 800,519, cl. F25B, 1979), realizing the given method and comprising, successively interconnected in a closed path of the refrigerant flow, an evaporator including interconnected suction header and at least two heat-exchange plates, each having at least one channel for the refrigerant to flow through, a means to separate the liquid refrigerant, connected thereto is a differential pressure relay having a pressure transducer, a compressor, a condenser, a receiver, and a means for pulse feeding of the liquid refrigerant.
However, the given method and apparatus to realize it, providing for the liquid refrigerant boiling temperature range being set as the difference between the temperature of the refrigerant vapour condensation and boiling temperature, entails a maximum difference between the liquid refrigerant condensation pressure and that of evaporation, which is conductive to an increase in the power consumption.
Moreover, the constant difference between the temperature of the refrigerated medium and the boiling point envisaged by said method and apparatus to implement it necessitates the lowest possible refrigerant boiling temperature to obtain the preset temperature of the refrigerated medium, which affects the reliability of the apparatus.
Furthermore, the amount of the liquid refrigerant fed according to said method depending on the temperature of the refrigerated medium at the beginning of the refrigeration process, a surplus thereof accumulates at the end of the process, which results in breakages, thereby affecting the reliability of the apparatus.
Besides, as the given method and apparatus to implement it provide for a smaller difference between the temperature of the refrigerated medium and the refrigerant maximum boiling temperature at the end of the refrigeration process, the amount of vapours being sucked and, accordingly, of the liquid refrigerant is reduced (which may force the vapours out of the condenser), which also affects the reliability of the apparatus.